Hi Carl H,
Thank you for your response.It's my grandmothers phone, a Samsung J4+. I exported her contacts today phone to sim. This issue only began after a recent software update. We have factory reset the phone and reentered her contacts and the issue remains. On the US Samsung community account, they advised to disable Call Protection and this seemed to resolve the issue. Unfortunately, I can not see anywhere such a function/app appears within the UK market.